<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title></title>
</head>
<body>
<div id="app"></div>
<script>
  let oEles = document.getElementById('app');
  let  oChildren = oEles.getElementsByTagName('p');
  console.log(oChildren);
  debugger;
  let oP = document.createElement('p')
  oEles.appendChild(oP)
</script>
</body>
</html>
